1. Technical Field
The present invention relates to a tire mold, to a method for molding a tire and to a resulting vehicle tire. In particular, the present invention relates to improvements in vacuum molding the tire.
2. Description of the Prior Art
Vacuum molding a tire is known. U.S. Pat. No. 4,573,894 discloses a tire mold having a cavity for receiving and shaping the tire. The cavity is defined by a surface for contacting the exterior of the tire during a tire curing cycle. The cavity is fluidly connected with a vacuum source for evacuating fluid from within the cavity during the early portion of a tire curing cycle. This evacuation process prevents fluid from becoming trapped between the tire and the surface defining the cavity. Visual defects in the form of voids in the tire exterior are, thus, eliminated. Furthermore, optimal curing contact between the surface defining the cavity and the exterior of the tire results. The advantages of such a vacuum molding system are recognized and are evidenced by the increasing use of vacuum molding in the tire curing art.
A tire mold cavity typically includes a plurality of projections which define pockets in the mold. The pockets form ground engaging tread elements about the outer circumference of the tire. U.S. Pat. No. 4,881,881 discloses an improvement to the vacuum molding system by venting laterally or circumferentially adjacent pockets through specially shaped arch-vent passages formed in the projections. Fluid may communicate between adjacent pockets and then to the vacuum source so the fluid does not become trapped in a pocket. Thus, a ground engaging tread element free from visual defects is provided by the use of arch-vent passages in the vacuum molding system.
Venting through an arch-vent passage has proved advantageous in a tire production environment. However, the use of the arch-vent passage has practical limitations. On a tire having a groove wider than approximately one-half inch, problems may arise during removal of the cured tire from the tire mold. Such a relatively wide groove is often found extending circumferentially on a performance tire or a light truck tire. The problem arises because an arch-vent remnant formed by cured rubber extending into the arch-vent passage may be sheared off during removal of the cured tire from the mold. This is a particular problem when the arch-vent passage is located in or near a plane extending radially of the tire.
The sheared-off arch-vent remnant then may fall into the bottom of the cavity in the tire mold. The arch-vent remnant then is cured into the subsequent tire that is placed in the tire mold which results in a visual defect referred to as a blemish. Thus, it will be apparent that it is desirable to produce a tire without any arch-vent remnants extending across such relatively wide and circumferentially extending groove in a tire.